1. Field of the Invention
The present invention relates to a method for polymerizing alpha-olefins, a catalyst for such a polymerization method and a method for producing such a catalyst. A particular aspect of the present invention relates to a method for preparing a catalyst which produces linear low density polyethylene (LLDPE) and high density polyethylene (HDPE) having a relatively broad distribution of melt flow ratios (MFR).
2. Description of the Prior Art
Linear low density polyethylene polymers possess properties which distinguish them from other polyethylene polymers, such as homopolymers of polyethylene. Certain of these properties are described in Anderson et al, U.S. Pat. No. 4,076,698.
Karol et al, U.S. Pat. No. 4,302,566, describes a process for producing certain linear low density polyethylene polymers in a gas phase, fluid bed reactor.
Graff, U.S. Pat. No. 4,173,547, Stevens et al, U.S. Pat. No. 3,787,384, Strobel et al, U.S. Pat. No. 4,148,754, and Ziegler, deceased, et al, U.S. Pat. No. 4,063,009, each describe various polymerization processes suitable for producing forms of polyethylene other than linear low density polyethylene, per se.
Graff, U.S. Pat. No. 4,173,547, describes a supported catalyst obtained by treating a support with both an organoaluminum compound and an organomagnesium compound followed by contacting this treated support with a tetravalent titanium compound.
Stevens et al, U.S. Pat. No. 3,787,384, and Strobel et al, U.S. Pat. No. 4,148,754, describe a catalyst prepared by first reacting a support (e.g., silica containing reactive hydroxyl groups) with an organomagnesium compound (e.g., a Grignard reagent) and then combining this reacted support with a tetravalent titanium compound. According to the teachings of both of these patents, no unreacted organomagnesium compound appears to be present when the reacted support is contacted with the tetravalent titanium compound.
Ziegler, deceased, et al, U.S. Pat. No. 4,063,009, describes a catalyst which is the reaction product of an organomagnesium compound (e.g., an alkylmagnesium halide) with a tetravalent titanium compound. The reaction of the organomagnesium compound with the tetravalent titanium compound takes place in the absence of a support material.
A vanadium-containing catalyst, used in conjunction with triisobutylaluminum, as a co-catalyst, is disclosed by W. L. Carrick et al in Journal of American Chemical Society, Volume 82, page 1502 (1960) and Volume 83, page 2654 (1961).
A majority of the aforementioned patents wherein an organomagnesium compound, a tetravalent titanium compound and/or a tetravalent vanadium compound are used to produce catalysts for polymerization of ethylene alone or in combination with 1-olefins (also known as alpha-olefins), teach the necessity of using only such amounts of the organomagnesium compounds that are necessary to react with the hydroxyl (OH) groups on the carrier. The catalysts produced in accordance with the teachings of the aforementioned patents yield polyethylene polymers having relatively narrow molecular weight distribution, as evidenced by relatively narrow melt flow ratio (MFR) values.
Accordingly, it is a primary object of the present invention to prepare a catalyst for polymerization of alpha-olefins which yields products of a relatively broad molecular weight distribution with very high activity in the absence of chlorine-containing modifiers.
It is an additional object of the present invention to provide a catalytic process for polymerizing alpha-olefins which yields linear low density polyethylene or high density polyethylene of a relatively broad molecular weight distribution.